Trying to use small inverter through cig. lighter adapter

Hi, I had the same problem. I have a 400 watt inverter. When running it with the supplied ciggy lighter type 12 volt receptacle it would either alarm on low voltage or shut down if it even ran anything at all. Problem was wires to the 12 volt receptacle were much too small. Solution was to mount the inverter inside a cabinet and hardwire it directly to the battery with 10 gage wire (fused of course). Now we can run 2 CPAPs with humidifiers all night. It takes about 20 ampere-hours for 8 hours of use. -Mark.